1. Field of the Invention
The present invention relates to a process for producing an .alpha.-hydroxyisobutyric acid. More particularly, it relates to a process for efficiently producing an .alpha.-hydroxyisobutyric acid by using an .alpha.-hydroxyisobutyric acid ester as the starting material. Since the .alpha.-hydroxyisobutyric acid is used as the starting material for producing methacrylic acid which is useful in industry, it is of great significance in industry to establish an economical process for producing .alpha.-hydroxyisobutyric acid.
2. Description of the Related Arts
As processes for preparing .alpha.-hydroxyisobutyric acid, (i) a process in which isobutylene is used as the starting material (German Patent No. 1,189,972), (ii) a process using isobutylene glycol as the starting material (J. Org. Chem., 23, 1488-9 (1958)), and (iii) a process in which acetone cyanohydrin, sulfuric acid and water are reacted and then subjected to hydrolysis (Japanese Patent Publication No. 61932/1988), have heretofore been known.
In the processes (i) and (ii), however, the yield of .alpha.-hydroxyisobutyric acid is insufficient, and a large amount of by-product is formed. Accordingly, if the total resultant of either process (i) or (ii) is used as the starting material, the yield of methacrylic acid as the final product comes to be greatly decreased. In the process (iii), the reaction solution contains acidic ammonium sulfate, so .alpha.-hydroxyisobutyric acid is difficult to be separated, and in addition, there is a problem of disposing of ammonium sulfate which results as by-product in at least an equal weight as that of the desired product, and accordingly, it is not an advantageous process for producing .alpha.-hydroxyisobutyric acid on an industrial scale.